i3: add shortcut for `workspace back_and_forth`
Switch from mplayer2 to mpv
mpv: do not use xv video driver as default

xv has issues with OSD.
vim: remove xkb.vim, as it is included in vim-runtime

Did I really have to add this in the first place?
zshrc: do not complete functions starting with an underscore
vim: stop worrying, remove useless garbage and use a plugin manager